Magnetic Bearings: An Attractive Force for Energy-efficiency
With sustainability and energy-efficiency targets tougher than ever, magnetic bearings are drawing the attention of engineers in many industries, offering a whole range of advantages from increased performance to extended lifespan.
In the industrial world today, priorities are changing. Increasingly, environmental impact and the cost of energy are influencing our priorities and the decisions we make. In addition, productivity, efficiency, minimizing variance, extending warranties and managing the total cost of ownership are driving consumers’ choices.
Our world and our livelihoods are increasingly tied to global conditions. Both financially and environmentally there are increasing benefits to be achieved by improving the efficiency and consistency with which we utilize our natural resources. SKF through its BeyondZero™initiative aims to increase the positive environmental impact of its solutions by offering new technologies, products and services with enhanced environmental characteristics. Customers want to ensure that they are buying products and equipment that are not only robust and reliable but innovative and sustainable. We are moving towards a more responsible industry, where products that can address all these needs are valued more highly than ever before.
With world water consumption expected to rise around 50% by 2020*, biological wastewater plants are looking for more effective, energy-efficient water treatment technologies. Aeration blower systems present a prime opportunity for asset improvement. (*Source: www.theworldwater.org)
A Aeration Blower Permanent Magnet Motor
Magnetic Bearings for Aeration Blower Systems
In traditional wastewater facilities, the aeration blower system can represent over 40% of the plant’s total energy use. Used to blow air into tanks so bacteria can break down organic waste, a typical mid-size aeration system operates with two to five air blowers. For each blower, energy use accounts for up to 80% of its total lifecycle costs.
Reducing the energy requirements of aeration blowers will help plants cut their energy costs and CO2 emissions. SKF’s high-speed permanent magnet motor solutions that utilize magnetic bearings are already making it possible.
Magnetic bearing systems represent an innovative approach to the support of rotating equipment, achieving performance levels not previously possible with traditional rolling element or fluid film bearing technologies. Magnetic bearings are a non-contacting technology, and as such they offer a range of important benefits, from almost zero friction, active vibration control, reduced energy consumption and the elimination of bearing wear. In addition, it is possible to operate at speeds that were unachievable with traditional technology. Magnetic bearings are ideal for use in processes that are sensitive to contamination since the need for lubrication and maintenance has been eliminated. For example, applications within the vacuum chambers of semiconductor manufacturing and hermetically sealed refrigeration compressors can and do benefit from the use of this technology.
Real-world success with SKF
A wastewater treatment facility in France
The variable speed blowers incorporating
One-year savings with the SKF solution:
How Magnetic Bearings Work
The concept behind magnetic bearings has been around for many years and for a long time the use of the technology was limited to extremely specialized, unique or ultra-high speed applications. Developments in magnetic bearing technologies along with advancements in computing power have seen a reduction in the size of control systems and increases in system performance making magnetic bearings an excellent choice for a number of industrial applications.
There are three key components in a magnetic bearing system that work together to achieve this new level of performance. First the magnetic bearing itself consists of stationary (stator) components as well as rotating (rotor) components. These components create the magnetic field that will support and control the rotor position. The second component is the position sensor. These sensors continuously monitor the position of the bearing rotor relative to the position of the bearing stator. The third component is the Magnetic Bearing Controller (MBC). This is the ‘brains’ of the system, taking the data from the position sensors and determining how much power it should deliver to each magnetic bearing in order to keep the system stable and under control.
The magnetic bearing stator consists of a stack of steel laminations that are wound with copper wire to form an electromagnet. In operation, a current is supplied to each coil of wire to produce an attractive force that levitates the shaft inside the bearing. The MBC applies the precise level of current to the coils determined by monitoring signals from the positioning sensors in order to keep the shaft at the desired position throughout the operating range of the machine. Depending on the application, there is typically a 0.5 to 1 mm air gap between the bearing rotor and stator.
The position sensor registers any change in position of the shaft (rotor). This change in position is communicated back to the MBC where the signal is processed; the controller decides what the necessary response should be, then initiates a response from the MBC’s amplifier. This response should then adjust the magnetic force in the corresponding electromagnet in order to bring the shaft back to center.
This process repeats itself over and over again. For many applications, the sample rate from the sensor can be 15,000 times per second, or 15 kHz. The sample rate is high because if the power to the magnet is left unchanged as the rotor moves closer to the magnet, the attractive force will increase as the gap decreases. So the system continuously adjusts the magnetic strength coming from the electromagnets in order to hold the rotor in the desired position.
The Application of Magnetic Bearings
For centrifugal air blowers, few technologies can match the energy efficiency and reliability that’s possible with a permanent magnet motor (PMM), active magnetic bearings (AMB) and a variable speed drive (VSD). SKF has designed this advanced combination of components and technologies as a complete package solution that can help manufacturers streamline product design, development and assembly.
Permanent magnet motor
- Low energy use and cooling requirements
- High-speed capabilities in a compact design
- 10%+ more energy efficient than conventional motors at full load and part load
- Direct drive configuration eliminates gearbox and oil
- Optimized shaft geometry accommodates large impellers with robust rotor dynamics
Active magnetic bearings
- Accommodate instant and frequent start-ups and transient surge forces
- Active control system provides vibration-free performance
- Capable of speeds in excess of 40 000 rpm
- Levitate rotating components for friction- and lubricant-free performance
- Unitized radial and axial bearing modules enable compact packaging and robust performance
Magnetic bearing controller
- Tracks and registers rotor position up to 15 000 times per second
- Controls rotor position to within a micron-sized orbit
- Continuously corrects rotor position by adjusting the power supplied to each electromagnet
- Instrumentation for integration into the blower control system
The data that is collected and analyzed by the MBC during normal operation can be used to help monitor and assess the performance of the system. Traditionally external vibration monitoring equipment would be required to collect this level of information but with magnetic bearings, it comes as part of the solution. Such active monitoring help not only to improve machine reliability, but also enable better decisions to be made based on what is known about a specific process. What you are able to measure, you are able to improve, so using the measurements captured here allows for troubleshooting and system enhancement activities.
By levitating the rotating components, SKF magnetic bearings enable a friction-free system that eliminates the need for lubrication. The result is a range of oil-free motor solutions that can deliver between 75 and 350 kW of power. As a leading global supplier of high-speed permanent motors, SKF can deliver complete standardized packages from a single source.
Compared to traditional lobe-type blowers, aeration blowers that utilize SKF high-speed permanent magnet motor solutions can offer:
Lower total cost of ownership (TCO)
- 10 to 40% lower energy use
- Improved service life and reliability
- exceeds mean time between failure (MTBF) rates of 100 000 hours
- Reduced component wear and less maintenance
- An oil-free environment with no risk of contamination
- Up to 30% lower noise levels
- A smaller, more lightweight footprint
- Compliance with environmental regulations
- Worldwide SKF service network support
SKF High-speed permanent magnet motor solutions are helping blower manufacturers design and develop the next generation of highly energy-efficient, highly reliable centrifugal air blower units. This solution combines the cutting-edge technology of a high-speed permanent magnet motor, active magnetic bearings with an integrated control system and a variable speed drive.
The PM Motors App from SKF
Download the PM Motors App from SKF from the Apple© App Store, scan the “trigger” image at left, and explorethe complete SKF portfolio of high-speed permanent magnet motor solutions!
Get more details at skf.com/PMmotors
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